As part of the surgical procedure commonly known as extracapsular cataract extraction, during which the anterior capsule is extracted with the lens and the posterior capsule is drained but left intact, an artificial lens is installed into the posterior capsule. As illustrated in FIGS. 1-3, the artificial intra-ocular lens (IOL) 1 is provided with two integrally formed appendages or haptics 2,3 which are designed to centrally mount the IOL while nesting into the inner peripheral rim 4 of the posterior capsule. It is estimated that in half of such surgical interventions, one of the haptics 2, 3 is not retained into the rim of the posterior capsule by its anterior flaps 5 and instead bears against the ciliary sulcus 6, or is erroneously implanted in that position, as illustrated in FIG. 1. This asymmetrical position of the IOL results in a decentration whereby the axis XX' of the IOL is shifted away from the actual axis Y--Y' of the eye. There results a loss of visual acuity which often evades the attention of the ophthalmologist.